1. Field of the Invention
This invention relates in general to bearings used in drilling and production equipment, and in particular to tuned bearings for use in motors driving electrical submersible pumps.
2. Prior Art
A submersible pump is a centrifugal pump having a submersible motor that rotates the shaft to drive the pump. The motors for high volume oil and water production may be from six to sixty feet in length and be rated at several hundred horsepower. Each motor has a stator secured within a tubular housing. The stator is made up of thin disks, called laminations that are magnetic and insulated from each other by coatings. Windings extend through the laminations to the stator.
A rotor secured to a shaft rotates within the stator. Because of the long length, the rotor is made up of a number of rotor sections. Each rotor section comprises a large number of flat metal disks, called laminations that are secured by copper rods. The disks are insulated from each other by coatings. The rotor sections are spaced apart from each other, and a bearing assembly is located between each rotor section to maintain the shaft in axial alignment. The rotor sections are keyed to the shaft for rotation with the shaft, but are axially movable with respect to the shaft.
Each bearing assembly includes a sleeve keyed to the shaft for rotation. A bearing body fits slidingly on the sleeve. An elastomeric ring, coil, or other mechanism encircles the bearing body in a groove acting to engage the stator and prevent the movement of the bearing body. The motor is filled with oil, and heated during operation, causing the elastomeric ring or other mechanism to expand and frictionally engage the inner wall of the stator. This engagement prevents the bearing body from rotating and supports the shaft in alignment.
As the motor begins to operate, the shaft will oscillate within the bearing according to the vibration frequency. Depending upon the oscillation frequency of the shaft, significant damage can occur to the bearing, shaft and stator bore due to vibration.